ION TRANSFER ANALYSIS OF EPHEDRINIUM ION AT LIQUID- LIQUID INTERFACE USING VOLTAMMETRY

• Main Author: Irdhawati
• Format: Dissertations
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/34609
• Institution: Institut Teknologi Bandung

Ephedrine hydrochloride [(1R-2S)-2-(methylamino)-1-phenylpropane-1-ol hydrochloride (Eph HCl) is a sympathomimetic drug that stimulates both - and -adrenergic receptors. It causes a rise of systolic and diastolic pressure, bronchodilation and mild stimulation of the central nervous system. Ion transfer at liquid-liquid interface is a fundamental process in drug absorption. This process can be described as a simple ion diffusion in a non homogeneous medium or chemical reaction involving ion transfer between two immiscible solution. Electrochemical techniques have been developed for studying charge transfer reaction at the interface between two immiscible solutions, as a simple model of biomembrane and an important basic in some analysis systems. In order to improve our understanding on drug absorption, this research aim to obtain a model of electrochemical cell on ephedrinium ion (EphH+) transfer and to study mechanism and kinetic of ephedrinium ion transfer at the interface of water and some organic solvents. EphH+ ion transfer at the interface of water and organic phase was studied using organic solvents having different dielectric constant, namely nitrobenzene (NB), 1,2-dichloroethane (1,2-DCE), and o-nitrophenyloctylether (NPOE). In voltammetric study, lithium chloride (LiCl) was used as supporting electrolyte in water phase. On the other hand tetrabutilammonium tetraphenylborate (TBATBP) and tetrabutilammonium tetrakis(4-chlorophenyl)borate (TBATClPB) were used as supporting electrolytes in organic phase. Methylephedrine hydrochloride (MeEph HCl), phenylpropanolamine hydrochloride (PPA HCl), paracetamol (PCT) and coffein (CAF) were used in selectivity study. MeEph HCl and PPA HCl are choosen because of the similarity of their structures with Eph HCl, while PCT and CAF are frequently used in combination with Eph HCl in pharmaceuticals. In this research cyclic voltammetry technique was used for determination of ion transfer and selectivity study of some interference ions, whereas differential pulse voltammetry technique was used for determination of optimum pH, detection limit, accuracy, and precision of measurements. Cyclic voltammogram of EphH+ ion showed that EphH+ ion transfer from aqueous phase to organic phase occured in potential window of supporting electrolyte solution. The faradaic peak current obtained in each organic solvents was different due to dielectric constant of the solvents, which is related to polarity of the solvents. This was indicated from the plot between concentration of Eph HCl or the square root of scan rate (v1/2) and peak currents. The slope of the curve showed that EphH+ ion transfer at the interface of water|NB > water|NPOE > water|1,2-DCE. These results were in accordance to the polarity of organic solvents having dielectric constant of 34.82; 24.2 and 10.36 for NB, NPOE and 1,2-DCE, respectively. Cyclic voltammograms of EphH+ ion transfer indicated that the process was reversible and diffusion controlled. The voltammograms were characterized by anodic and cathodic peak potentials (Epa and Epc), anodic and cathodic peak currents (Ipa and Ipc), half-wave potential (Epm), and peak-separation potential ( Ep). The Epa shifted to more positive potential and Epc shifted to more negative potentials linearly with the increasing of v1/2 due to uncompensated resistance in organic phase and undesirable polarization at reference electrode. The extrapolated values of Epa and Epc at v = 0 resulted in corrected peak potential because uncompensated resistance in the organic phase, independent of both the concentration and scan rate. The corrected Ep value confirmed that EphH+ is a monovalen cation. The diffusion coefficient of ephedrinium ion transfer was determined using Randles-Sevcik equation. The calculated values were 2.9 x 10-6 cm2/s, 1.1 x 10-7 cm2/s, and 1.0 x 10-5 cm2/s at water|NB, water|1,2-DCE, and water|NPOE interfaces, respectively. Tetramethylammonium chloride (TMACl) was used as standard compound in the determination of standard potential ( w 0 Eph) and Gibbs free energy ( G 0,o w ) of EphH+ ion transfer from aqueous phase to tr ,Eph organic phase. The standard potentials of the ephedrinium ion transfer were 0.063 V; 0.111 V and 0.160 V at the water|NB, water|1,2-DCE, and water|NPOE interfaces, respectively. The Gibbs free energy were 6.079 kJ/mol; 10.710 kJ/mol; dan 15.438 kJ/mol at the water|NB, water|1,2-DCE, and water|NPOE interface, respectively. From four compounds used in selecticity study using separated solution method, namely MeEph HCl and PPA HCl, PCT and CAF, only the first two compounds that gave voltammograms peaks because MeEph HCl and PPA HCl were in a salt form that can be ionized to MeEphH+ and PPAH+ ions, respectively. While PCT is a weak electrolyte and CAF is not ionized in aqueous solution. The result of pH optimization at the interface system for EphH+ determination was obtained at pH of 7 in water|1,2-DCE system, and at pH of 9 in both of water|NB and water|NPOE systems. The pH values were close to pKa value of EphH+ ion, which is 9.2. The detection limits of EphH+ ion obtained from calibration curve in concentration range of 10µ M - 80µ M were 2.4µ M; 3.7µ M; and 3.6µ M, respectively in water|NB, water|1,2-DCE, and water|NPOE system. The precision of the measurements obtained from 20 repeated mesurements, resulted in the Horrat of less than two. Percent recovery of sample analysis was determined by calibration curve method, the result was found between 95.6% to 100.5% showing good accuracy of analysis. The results provide informations that improve our understanding on EphH+ ion transfer analysis at liquid-liquid interface in term of electrochemical cell design and analytical performance of electrode. The results also show the mechanism and ion transfer kinetic involving the diffusion coefficient, standard potential of ion transfer, and Gibbs free energy of the interface system for EphH+ determination. This research is expected to provide important information to the development of electroanalytical chemistry.